This invention relates to the storage of combustible gases in pressure vessels, and more particularly to preventing buildup of excessive pressure in the vessel while preventing the emission of the combustible gases into the environment.
It is known to store combustible gases such as hydrogen, methane etc. under pressure in suitable pressure vessels. In some instances, the gases are stored in the gas phase under moderately high pressures. In other instances, the gases may be stored in the liquid phase under higher pressures and lower temperatures.
Pressure vessels have a maximum allowable pressure tolerance, and the gas pressure within the vessel must be kept below that pressure to insure the integrity of the vessel. The pressure within the vessel varies with the amount of heat transferred into the vessel from the outside. While thermal insulation can be used to minimize such heat transfer, it is inevitable that some heat will be transferred into the vessel causing a pressure rise therein. For stationary applications, the vessels can be made with extra material (e.g. metal or fiber reinforced plastic) to accommodate the pressure rise, and to otherwise provide extra vessel strength without any great sacrifice. For mobile applications (e.g. fueling vehicles) however, the extra material undesirably consumes more space and adds more weight to the vehicle. Smaller, lighter-weight vessels can be employed for mobile applications if the pressure within the vessel can be managed so as to keep it below the maximum pressure tolerance of the lighter-weight vessels.
The present invention (1) manages the pressure of a combustible gas within a pressure vessel by venting the vessel to keep the pressure therein below the vessel""s maximum pressure tolerance while, at the same time, (2) prevents undesirable combustible gas emissions from escaping to the environment. More specifically, the invention contemplates apparatus for storing a combustible gas that includes (i) a pressure vessel for containing the gas under pressure, which vessel has a maximum allowable pressure tolerance, (ii) a pressure relief valve communicating with the vessel for venting the gas before the vessel""s pressure tolerance is reached, and (iii) a catalytic reactor communicating with the pressure relief valve for catalytically combusting combustible gas exiting the relief valve with air so as prevent emission of the combustible gas into the environment. The catalytic reactor preferably comprises at least one catalytic diffusion burner and a housing surrounding the burner wherein (a) the catalytic burner comprises a microporous body, a combustion catalyst on a surface of the body, and a first inlet for admitting the gas to the microporous body for diffusion through the microporous body and reaction with air on the catalyst, and (b) the housing has a second inlet for admitting air to the burner and an outlet for exhausting combustion gases to the environment. More preferably, the microporous body comprises a tube having a microporous wall, and the inlet supplies the combustible gas to the center of the tube for radial diffusion through the porous wall. The microporous tube surrounds a perforated gas distribution pipe that distributes the gas substantially uniformly along the length of the microporous tube. Most preferably, the apparatus includes a second catalytic burner downstream of the one catalytic burner for receiving exhaust gas from the one burner and catalytically combusting any uncombusted combustible gas that might be contained therein. According to a most preferred embodiment, the apparatus further includes an igniter downstream of the catalytic burner(s) to ignite any uncombusted combustible gas passing through said the burner(s) to heat-up the burner and light-off the catalyst at start-up, and otherwise ignite any residual combustible gas remaining in the combustion gases from the burner(s).
The invention will be better understood when considered in the light of the following detailed description of a preferred embodiment thereof which is given hereafter in connection with the attached drawings in which: